With Mendelian randomization a genotype can be used as an instrumental variable if it is causally linked to the trait (usually as part of a genome-wide “associa

With Mendelian randomization a genotype can be used as an instrumental variable if it is causally linked to the trait (usually as part of a genome-wide “association” study)—lung cancer in this case. this can provide reasonable assurance of causality. See Book of Why.